1. Technical Field
This invention relates to a hard real-time processing unit for processing hard real-time processing steps. More specifically, at least one processor in a multiprocessing system is designated as a hard real-time unit for processing real time processing steps of a task and at least one processor in the system is designated as a non-hard real-time unit for processing non-hard real-time processing steps of a task.
2. Description of the Prior Art
General operating systems may be classified into three general categories associated with completion of a task or processing steps of a task within a predefined time interval. The three general categories are known as hard real-time operating systems, soft real-time operating systems, and non-real-time operating systems. A hard real-time operating system guarantees processes will complete in a defined amount of time. Processing steps in a hard real-time operating system are known as deterministic operations. The terms hard real-time processing steps and deterministic operations are used interchangeably. In hard real-time systems, if a processing step completes correctly but takes longer than its given amount of time, the process fails. A soft real-time system is less restrictive than a hard real-time system. In a soft real-time system, critical processes are given priority over non-critical processes. The boundaries in a soft real-time system are less severe than those in a hard real-time system. For example, in a soft real-time system if a process completes correctly but takes longer than its given amount of time, the result may still be useful. However, in a hard real-time system, if a process completes correctly but takes longer than its given amount of time, the result will not be useful. In a non-hard real-time system, the processing steps are non-deterministic operations and as such are not subject to real-time processing constraints. The terms non-hard real-time processing steps and non-deterministic operations are used interchangeably. In soft real-time, hard real-time, and non-hard real-time systems, a scheduler is utilized to guarantee the amount of time a process requires for execution. The scheduler is part of the kernel in an operating system that initiates and terminates processes and threads. In addition, the scheduler may periodically decide which thread should be run next and switch control to that thread.
There are different real-time operating systems available, many with their own peculiar niche and their own peculiar application program interface. For example, U.S. Patent Publication 2002/0078121 to Ballantyne provides a general purpose operating system in which the entire operating system is treated as a single real-time thread. There is no support for a general purpose operating system in which processors and processes are categorized according to real-time and non-real-time scheduling needs. Rather, real-time scheduling is implemented for non-real-time processes. There is no support in Ballantyne for a single general purpose operating system that supports distinguishing and respecting hard real-time and non-hard real-time processing of appropriately distinguished processing steps. Similarly, U.S. Pat. No. 6,148,389 to So relates to a digital signal processor that runs real-time functions. The digital signal processor is attached to a system running a general purpose operating system. However, the digital signal processor of So has a separate kernel from that of the general purpose operating system. There is no support in So for a single operating system, having one kernel, that can distinguish between hard and soft real-time processes and offload the categorized process to a respectively categorized processor.